It is known in the pharmaceutical art to prepare compositions which provide for slow release of pharmacologically-active substances contained in said compositions after oral administration to humans and animals. Such slow-release compositions are used to delay absorption of a medicament until it has reached certain portions of the alimentary tract. Such controlled release of a medicament in the alimentary tract further maintains a desired concentration of said medicament in the blood stream for a longer duration than would occur if conventional rapid release dosage forms are administered.
A controlled-release formulation comprising a matrix having dispersed therein both the pharmacologically-active salt form of a medicament and the free base form of the same medicament is described in U.S. Pat. No. 4,443,428. In each of the formulations described therein, the amount of excipients is in excess of 20% by weight. A similar formulation, but one that is based upon varying the water solubility of the active medicament, is described in WO-A-8102975.
Controlled-release formulations containing mixed esters of a medicament are described in FR-A-2571371.
Derwent abstracts a European patent application where a mixture of crystalline diasteromeric salts of a medicament causes production of isomers to produce a sustained release effect.
Ceftiofur (Formula I) is a known cephalosporin antibiotic, and is disclosed in U.S. Pat. No. 4,464,367.